Mycobacterium tuberculosis (Mtb) regulates lung macrophage activation and function, including the balance of pro-inflammatory and anti-inflammatory mechanisms that affect pulmonary immune responses and the outcome of infection. We propose that optimum host response and containment of infection requires proper regulation of the inflammatory balance. Better understanding of this balance and how it is regulated will advance our understanding of how Mtb evades host immunity and the problems of latent infection and disease progression. We propose that factors downstream of Toll-like receptor 2 (TLR2) contribute to regulation of this balance; among these are Tpl2, ERK and KLF4, which we propose promote expression of IL-10, induce other anti- inflammatory mechanisms, and contribute to inhibition of macrophage MHC-II antigen presentation, thereby regulating both innate and adaptive immunity to Mtb. We will study markers of lung macrophage inflammatory state and function; a central paradigm will be the balance of IL-10 and IL-12, which are anti-inflammatory and pro-inflammatory mediators, respectively. We will use knockout and floxed gene models (for cell lineage- specific knockout) to focus studies on lung macrophages, as well as pharmacologic tools, to test the role of Tpl2, ERK and other molecules in regulating the inflammatory balance of lung macrophages during infection with Mtb. We will use both human and mouse models to study regulation of lung or alveolar macrophages. Aim 1 will determine the roles of TLR2 and other receptors pathways in regulating the ERK pathway and the inflammatory balance of lung macrophages during responses to Mtb. Aim 2 will determine the roles Tpl2, ERK and downstream mechanisms (e.g. KLF4) in regulating the inflammatory balance of lung macrophages during responses to Mtb. Aim 3 will determine the roles of Tpl2, ERK1/2 and KLF4 in regulation of macrophages and host immunity in vivo.